The contractile proteins, actin and myosin, play an important role in the function of muscle and nonmuscle cells. In smooth muscle, phosphorylation of the 20 kDa myosin light chain initiates contraction. In nonmuscle cells, such as rat basophil leukemic cells, phosphorylation of myosin is associated with secretion and changes in the cell shape. The goal of these experiments is to identify the various kinase(s) capable of phosphorylating myosin in activated T-cells and the possible physiological role of this phosphorylation in the function of T-cells. We have used T-lymphocytes (Jurkat cell line) to examine myosin phosphorylation. Our results indicate that treatment of Jurkat cells by phorbol ester (PMA), a tumor promoting factor, results in incorporation of phosphate in both the myosin heavy chain and the 20 kDa light chain. Two-dimensional peptide maps of phosphorylated myosin heavy chains showed a new phosphopeptide in PMA treated cells suggesting the activation of protein kinase C. We will continue this project by examining myosin phosphorylation in T-lymphocytes that contain IL-2 receptors. We are specifically interested in determining whether or not tyrosine kinase(s) and/or serine/threonine kinase(s) phosphorylate myosin heavy chains and/or light chains in response to IL-2 and, if they do, which site(s) are phosphorylated. We are also interested in the role that IL-2 mediated phosphorylation of myosin might play in activation of T-cells.